Functional Magnetic Resonance Imaging ;Functional Magnetic Resonance Imaging ;What is it and what can it do?What is it and what can it do?

Heather RuppCommon Themes in Reproductive Diversity

Kinsey InstituteIndiana University

Note- Most slides were taken from Jody Culham’s fMRI for Dummies web site

Today

I. Structural Scans

II. Functional Scan

III. Simulator

IV. Study Design

Today

I. Structural Scans

II. Functional Scan

III. Simulator

IV. Study Design

Structural

• Different Pulse Sequences (T1, T2, EPI)

• Different Views

• Think about how to optimize scans for certain brain regions that may interest you

Magnetic Resonance Imaging (MRI)

T1 and TR

Source: Mark Cohen’s web slides

T1 = recovery of longitudinal (B0) magnetization• used in anatomical images• ~500-1000 msec (longer with bigger B0)

TR (repetition time) = time to wait after excitation before sampling T1

T2 and TE

Source: Mark Cohen’s web slides

T2 = decay of transverse magnetizationTE (time to echo) = time to wait to measure T2 or T2* (after refocusing with spin echo or gradient echo)

T1 T2

Today

I. Structural Scans

II. Functional Scan

III. Simulator

IV. Study Design

Functional Magnetic Resonance Imaging (fMRI)

First Functional Images

Today

I. Structural Scans

II. Functional Scan

III. Simulator

IV. Study Design

How Attractive?

1 = Very Unattractive2 = Unattractive3 = Attractive4 = Very Attractive

Today

I. Structural Scans

II. Functional Scan

III. Simulator

IV. Study Design

Subtraction LogicCognitive subtraction originated with reaction time experiments (F. C. Donders, a Dutch physiologist).

Measure the time for a process to occur by comparing two reaction times, one which has the same components as the other + the process of interest.

Assumption of pure insertion: You can insert a component process into a task without disrupting the other components.

Widely criticized

Example:

T1: Hit a button when you see a lightT2: Hit a button when the light is green but not redT3: Hit the left button when the light is green and the right button when

the light is red

T2 – T1 = time to make discrimination between light color

T3 – T2 = time to make a decision

Change only one thing between conditions!

Two paired conditions should differ by the inclusion/exclusion of a single mental process

How do we control the mental operations that subjects carry out in the scanner?

i) Manipulate the stimulus• works best for automatic mental processes

ii) Manipulate the task• works best for controlled mental processes

DON’T DO BOTH AT ONCE!!!

Source: Nancy Kanwisher

Dealing with Attentional Confounds

fMRI data seem highly susceptible to the amount of attention drawn to the stimulus or devoted to the task.

Add an attentional requirement to all stimuli or tasks.

How can you ensure that activation is not simply due to an attentional confound?

Time

Add a “one back” task• subject must hit a button whenever a stimulus repeats• the repetition detection is much harder for the scrambled shapes • any activation for the intact shapes cannot be due only to attention

Other common confounds that reviewers love to hate:• eye movements• motor movements

Block Designs

Assumption: Because the hemodynamic response delays and blurs the response to activation, the temporal resolution of fMRI is limited.

= trial of one type (e.g., face image)

= trial of another type (e.g., place image)

WRONG!!!!!

Blocked Design

Blocked vs. Event-related

Source: Buckner 1998

Thought Experiments• What do you hope to find?  • What would that tell you about the cognitive process involved?  • Would it add anything to what is already known from other techniques? • Could the same question be asked more easily & cheaply with other techniques?• Would fMRI add enough to justify the immense expense and effort?  • What would be the alternative outcomes (and/or null hypothesis)?  • Or is there not really any plausible alternative (in which case the experiment may not be worth doing)?  • If the alternative outcome occurred, would the study still be interesting?  • If the alternative outcome is not interesting, is the hoped-for outcome likely enough to justify the attempt?  • What would the headline be if it worked?• What are the possible confounds?• Can you control for those confounds?• Has the experiment already been done? 

Questions?

Top Ten Things Sex and Brain Imaging Have in Common

10. It's not how big the region is, it's what you do with it.

 9. Both involve heavy PETting.

 8. It's important to select regions of interest.

 7. Experts agree that timing is critical.

 6. Both require correction for motion.

 5. Experimentation is everything.

 4. You often can't get access when you need it.

 3. You always hope for multiple activations.

 2. Both make a lot of noise.

 1. Both are better when the assumption of pure insertion is met.

Source: students in the Dartmouth McPew Summer Institute